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Over a hundred academics recently signed a letter to British Journal of Sports Medicine and BMJ editors criticising them for their “pro-butter” stance and for publishing a “biased” editorial which claimed that the effect of saturated fats on cardiovascular health was grossly exaggerated. A rebuttal followed. What should have been a sensible scientific debate degenerated into a dispute over bias, integrity, and beliefs.

There is certainly a touch of the religious wars about these debates, and much of this is because of who controls the sacred nutritional guidelines. The current guidelines in the US and UK are similar. Both have areas of common consensus that few disagree with—such as eating fewer calories, eating more plants, eating less processed food, and drinking fewer sugary drinks—but when it comes to saturated fat, there is much less consensus.

The fat-diet-heart hypothesis is far from simple. The original idea that cholesterol in food was to blame …